1. Field of the Invention
The present invention relates to a ferrite core and a bobbin corresponding the ferrite core used in a coiled component for various electronic equipments, and to a transformer including the ferrite core and the bobbin.
2. Discussion of the Background
Used in a coiled component mounted in office machinery and appliances, a ferrite core is known in the related art, which includes an end face portion, a pair of outer legs protruding from both sides of the end face portion, and a center leg protruding from the end face portion between the outer legs. The conventional ferrite core's center leg has a circular, polygonal, elliptical, or oval cross section, and an inductor, such as a choke coil, or a transformer is configured by inserting the center leg into a wound body with wire wound of a bobbin.
A ferrite core 40 for a transformer is disclosed in Patent Document 1 and 2, which has an elliptical or oval cross section in order to achieve a small-sized and thin transformer, as shown in FIG. 21. In FIG. 21, a reference numeral is given to each part as follows, outer legs 42 of the core 40, a bobbin 43, a wound body 44 of the bobbin 43, first and second winding wire terminal blocks 45 and 46 of the bobbin, respectively, a winding wire 47 around the wound body 44, a first terminal 49 connected with the first winding wire, a second terminal 50 connected with the second winding wire, first and second ports 51, 52, respectively.
[Patent Document 1] JP-UM-B-3-53462
[Patent Document 2] JP-UM-A-5-87918
A center leg in a conventional ferrite core has a circular, polygonal, elliptical, or oval cross section. For example, when the center leg' cross section is elliptical as shown in FIG. 23, magnetic leakage flux φ1 and φ2 is uniformly generated by current through a wire (not shown) at both ends of a center leg 41 in a core, reference numerals 42 represents an outer leg.
The magnetic leakage flux φ1 and φ2 generated at both sides of the conventional core 40 is uniform and affects an adjacent circuit component by noise. In particular, a flyback transformer in electronic equipment has a gap between the center legs of the core, therefore, a large amount of magnetic leakage flux is generated from the gap. Accordingly, excess current is generated in a conductor composing a terminal or signal wire of the adjacent circuit component, thus it prevents improving properties of the circuit component. A circuit component affected by the noise is required to be positioned apart from transformer, as a result, it is difficult to manufacture a small-sized electric and electronic equipment, such as a power device, using the circuit component. Further, a shield, such as a shield wire, a shield plate, or a shield cover, is needed for preventing the magnetic leakage flux, thereby increasing cost.
As shown in FIG. 21, when the center leg 41 has an oval or elliptical cross section, since a distance between the center leg 41 and the outer legs 42 is constant throughout the periphery of the center leg, a distance G7 at the first winding wire terminal block 45 is the same as a distance G8 at the second winding wire terminal block 46 between the left and right outer legs (G7=G8).
In recent years, as electronic equipment, such as appliances, has had multiple functions, second winding wires involved increases and ports for the second winding wires led to the second winding wire terminal block 46 in the terminal 50 connected with the second winding wires increases. In FIG. 21, the ports of the second winding wire 52 are led to the left and right end portions of the second winding wire terminal block 46, as a result, an insulating distance d between the second port and the outer leg 42 of the core 40 is not sufficient. Accordingly, the second port 52 at the outer leg 42 is coated with a tube or tape for insulation, thus the structure is complicated for leading the ports. It takes much time to connect the winding wire to the terminal 50 in the port, therefore, working efficiency is reduced.
Considering the above-mentioned problem, as shown in FIG. 22, a distance G8 between the outer legs 42 at the second winding wire terminal block 46 is set larger than a distance G7 between the outer legs 42 at the first winding wire terminal block 45(G7<G8). However, since the distance between the outer leg 42 and the center leg 41 is not constant, magnetic flux tends to concentrate at an area where the center leg 41 and the outer leg 42 are relatively close. As a result, magnetic saturation is likely to occur, and in a converter transformer, its overlapping property deteriorates under overlapping condition of direct current and alternating current.
In the above example in the related art, a vertical-type transformer is disclosed, in which the center leg 41 or outer legs 42 vertically protrudes from a base plate, however, the above-mentioned problems also appear in a horizontal-type transformer in which a ferrite core is mounted parallel to the base plate.